The murder of Dr. George Tiller this weekend has reignited the controversy over late-term abortions. Tiller, one of the few providers of the procedure in this country, was gunned down Sunday on his way to church in Wichita, Kan. Both the pro-choice Planned Parenthood and pro-life Operation Rescue have issued statements denouncing Tiller's murder.

The tragedy left us wondering: What exactly is a late-term abortion? Click here to find out the facts after the jump.

The procedures that Tiller performed and was targeted for are not the usual first-trimester abortions one usually thinks of with pregnancy termination. Late-term abortions occur during the second or third trimester and are pretty rare. According to the Guardian, Tiller's clinic was one of only three in the United States to perform abortions after the 21st week of pregnancy.

Why is the procedure so rare? It's illegal in many states. There are 36 states that prohibit abortion after a certain point in pregnancy. (23 of those ban it after the fetus is viable.) Some states permit it if the woman's health is being compromised.

Late-term abortion is especially controversial because there is a chance the fetus could be viable outside the womb. Pro-life advocates consider this an especially heinous form of murder.

The pro-choice camp argues that late-term abortions are really a procedure of last resort. Writer Gretchen Voss shared her 2003 experience with a second-trimester termination in 2004. Her fetus had an open neural tube defect, meaning the spine had not closed properly and her child would have been born paralyzed and with severe birth defects if the baby lived at all. She called the termination "our last parental decision."

What's certain is that with this tragedy, the controversy isn't going to die down any time soon.